An example of a known vertical movement apparatus for a vehicle seat is disclosed in U.S. Pat. No. 4,790,597. The disclosed vertical apparatus has a seat bracket which supports a seat member, a floor bracket which is supported on a floor member and a link which is disposed between the seat bracket and the floor bracket. In addition, an end of the seat belt is connected with the vertical apparatus. The end of the seat belt includes an anchor member and a pawl member. The anchor member includes a latch which is connected with the seat bracket. One end of the pawl is rotatably connected with the link and the pawl has a plurality of teeth adapted to engage the latch. When a load exceeding a predetermined level is applied to the seat belt, the latch and the pawl are engaged to prevent the seat bracket from moving upward.
Another known vertical movement apparatus for a vehicle seat is disclosed in German Patent Laid-Open Publication No. 44 08 219 A1. The vertical movement apparatus described in this publication includes a link or a wire. One end of the link or wire is connected to a seat member and the other end of the link or wire is connected to an upper rail of the seat slide mechanism forming part of the floor member. The link or wire is fully extended at the top position of the seat bracket so that the vertical apparatus regulates the top level of the seat bracket.
Regardless of the position of the seat, with the aim of holding a tie of the seat belt, it is desirable that the end of the seat belt be connected with the seat member. However, with the constructions described above, if an excessive load is applied to the seat belt, the vertical movement apparatus do not prevent the seat member from moving in the upward direction. For example, with respect to the vertical apparatus disclosed in the above noted U.S. patent, when an excessive load is operated on the seat belt, the latch and the pawl are immediately engaged. As the pawl is connected with the link, the seat member is moved in the upward direction until reaching the top position of the seat member. Because the vertical apparatus receives the excessive load at the top position of the seat member, the parts forming the vertical apparatus have to be made of high strength material. Another example shown in the U.S. patent has a guide always slidably contacting the pawl side member and including many parts. On the other hand, with respect to the vertical movement apparatus disclosed in the above-mentioned published German patent, when the load is operated on the seat belt, there is no mechanism to hold the seat position so that the seat member is moved in the upward direction until the seat member reaches the top position. Because the vertical movement apparatus receives the excessive load at the top position of the seat member, the parts forming the vertical movement apparatus are made of high strength material.